DOA -,TTO

o

o ²

Data Out A, Teletype Output

3

AC

I

o

5 6

o

7 8

F

o o

o o

I

9 10 11 12 13 14 15

Load the contents of AC bits 8-15 into the teletype output buffer, and perform the function specified by F.

Setting Output Busy turns on the transmitter, causing it to send the contents of the output buffer serially to the teletype (the buffer is cleared during transmission). The printer prints the character or performs the indicated control function. If the punch is on, the character is also punched in the tape, with AC bit 15 cor-responding to channel 1 (a 1 in AC produces a hole in the tape). Completion of transmission clears Output Busy and sets Output Done, requesting an interrupt if Output Interrupt Disable is clear.

NOTE

Although the buffer clears during transmission, giving an NIOS without loading it again does not transmit a zero character. So do not give an NIOS without first loading the buffer. To transmit any character including null, either give a DOAS or give a DOA followed by an NIOS.

CAUTION

Clearing Output Busy while the transmitter is running (as with an NIOC) terminates the transmission. But the printer still prints whatever character is repre-sented by the indeterminate code it receives.

Timing. Models 33 and 35 can type or punch up to ten characters per second. After Owtput Done is set, the program has 4.55 ms to give a DOAS to keep typing or punching at the maximum rate. The 37 can handle fifteen characters per second, 66.7 ms. per chal'acter. After Output Done is set, the program has 3.33 ms to send a new character to maintain the maximum typing rate.

3-2

The sequence carriage return-line feed, when given in that order, allows sufficient time for the type block

Transfer the contents of the input buffer into AC bits 8-15, and perform the function specified by F. Clear AC bits 0-7.

Reception from the keyboard requires no initiating action by the program; striking a key transmits the code for the character serially to the input buffer. However, if the reader is under program control, giving the start function (NIOS or DIAS) sets Busy and causes the reader to read all eight channels from the next line on tape and transmit the line serially into the buffer (the presence of a hole produces a 1 in the buffer). In either case completion of reception clears Input Busy and sets Input Done, requesting an interrupt if Input Interrupt Dis-able is clear. When the character is brought into AC, tape channell corresponds to AC bit 15.

Consider this loop for typing out (we assume the printer is not in use).

OUT: DOAS

OUT: SKPBZ TTO previous (perhaps unknown to us) teletype output operation is finished.

The same dichotomy exists for input operations. This is bad:

IN: NIOS

I

Operation

A KSR is actually two indepeni:.lent devices, keyboard and printer, which can be operated simultaneously.

An ASR is really four devices, keyboard, printer, reader and punch, which can be operated in various combi-nations. Power must be turned on by the operator. On the 33 and 35 the switch is beside the keyboard and is labeled LINE/OFF/LOCAL or ON/OFF and has an unmarked third position opposite ON. A similar switch is located beneath the stand on the 37. When this switch is set to LOCAL or the unmarked position, power is on but the machine is off line and can be used like a typewriter. Moreover, in an ASR, turning on the punch allows the operator to punch a tape from the keyboard, and running the reader allows a tape to control the printer (if the punch is also on, it duplicates the tape).

Turning the switch to LINE or ON connects the unit to the computer and separates its input and out-put functions. Thus any information transmitted to the comout-puter from the keyboard affects the printer only in-sofar as the computer sends it back. Turning on the reader places it under program coptrol, and turning on the punch causes it to punch whatever is sent to the printer by the computer.

The only control on the reader is a 3-position switch. When the switch is in the FREE position, the tape can be moved by hand freely through the reader mechanism. The STOP position engages the reader clutch so the tape is stationary but the reader is still off. Turning the switch to START causes the reader to read the tape if the unit is in local, but places it under program contr;>l if on line.

The operator controls the punch by means of four pushbuttons. The two on the right turn the punch on and off. Pressing the REL. button releases the tape so it can be moved by hand through the punch mechanism.

Pressing B. SP. moves the tape backward one frame so the operator can delete a frame that is incorrect by striking the rubout key. Pressing HERE IS with the keyboard in local punches twenty lines of blank tape (lines with only a feed hole punched).

The keyboard resembles that of a standard typewriter. Codes for printable characters on the upper parts of the key tops on the 33 and 35 are transmitted by using the shift key; most control codes require use of the control key. Those familiar with the 33 or 35 who are using the 37 for the first time should take a close look at the keyboard. On the 37 the shift is used for real upper case characters. The control key is used for some control characters, but many have separate keys. Note also that both the keyboard arrangement and the labels differ somewhat. On all models the line feed (labeled "new line" on the 37) spaces the paper vertically at six lines to the inch, and must be combined with a return to start a new line. The local advance (feed) and return keys affect the printer directly and do not transmit codes. Appendix E lists the complete teletype code, ASCII characters, key combinations, and differ~nces among the several models.

On the 33 and 35 is a repeat button REPT. Pressing this button and striking any character key causes transmission of the corresponding code so long as REPT is held down. Characters that require the shift key may also be repeated in this manner, but there is no repetition of control characters.

Teletype manuals supplied with the equipment give complete, illustrated descriptions of the procedures for loading paper and tape, changing the ribbon, and setting horizontal and vertical tabs. Setting tabs is usually left for maintenance personnel; in any event, the best and easiest way to learn how to do any of these things is to have someone who knows show you how. However, as a precautionary measure we describe here the things you may have to do your·self.

Tltpe. The tape moves in the reader from back to front with the feed holes closer to the left edge. To load tape, set the switch to FREE, release the cover guard by opening the latch at the right, place the tape so that the sprocket wheel teeth engage the feed holes, close the cover guard, and set the switch to STOP.

To load tape in the punch, raise the cover, feed the tape manually from the top of the roll into the guide at the back, move the tape through the punch by turning the friction wheel, then close the cover. Turn on the punch with the unit in local and punch about two feet of leader by pressing HERE IS or the control, shift and P keys to generate null codes.

3-5

Paper. The 33 printer has an 8th-inch roll of paper at the back. Printed sections can be torn off against the edge of the glass window in front of the platen. To replenish the paper, snap open the cover, remove the old roll and slip a new one in its place. Draw the paper from the roll around the platen as in an ordinary typewriter.

The 35 and 37 printers have a sprocket feed and use 8Yz X 11 fanfold form paper. The supply is held in a tray at the back. To replenish it, first remove the upper cover by pressing the cover release button on the right side. To free the remaining old paper for removal, lift the paper guides by pushing the handle .marked PUSH at the right of the platen. To insert new paper from the tray, bring it up below the platen at the rear, line up the holes at the edges of the paper with the sprockets, and press line feed (in local) to draw the paper under the platen.

Ribbon. Replace the ribbon whenever it becomes worn or frayed or the printing becomes too light. Dis-engage the old ribbon from the ribbon guides on either side of the type block, and remove the reels by lifting the spring clips on the reel spindles and pulling the reels off. Remove the old ribbon from one of the reels and replace the empty reel on one side of the machine; install a new reel on the other side. Push down both reel spindle spring clips to secure the reels. Unwind the fresh ribbon from the inside of the supply reel, over the guide'roller, through the two guides on either side of the type block, out around the other guide roller, and back onto the inside of the takeup reel. Engage the hook on the end of the ribbon over the point of the arrow in the hub. Wind a few turns of the ribbon to make sure that the reversing eyelet has been wound onto the spool. Make sure the ribbon is seated properly and feeds correctly in operation.

3.2 PAPER TAPE READER

Two high speed readers, both of which process 8-channel perforated paper or mylar tape photoelectrically, are regularly available for use with the Nova computers. The 4011A is a sprocket-feed type that operates at speeds up to 150 lines per second; the 4011B is a brake-clutch type that can read up to 300 lines per second.

Except for timing considerations, the programming for both readers is identical: each uses only one 10 transfer instruction to retrieve data from an 8-bit buffer in the interface. Busy and Done are controlled or sensed by bits 8 and 9 in all 10 instructions with device code 12, mnemonic PTR. Interrupt Disable is controlled by interrupt priority mask bit 11.